Immersion Curing Process

ABSTRACT

A system and method for manufacture of prosthesis shells using a hot liquid bath to cure the shells is described. The shell is formed on a mold or mandrel, and is then immersed in a hot liquid bath to cure the shell material. Multiple layers of material, such a silicone, may be formed by immersing the layer into a hot liquid bath, cooling the cured layer, applying another layer of uncured material to the cured layer, and then curing the uncured layer in a hot liquid bath. A textured surface may be imparted to the shell by incorporating a texture component into the last layer formed, such that immersing the uncured layer incorporating the texture component in the hot liquid bath cures the last layer formed and dissolves the texture component.

BACKGROUND

The present invention is directed to the art of curing thin silicone sheets. More particularly, the invention is directed to a method of curing the silicone elastomer shell of a dip formed breast prosthesis.

Various methods have been employed to manufacture breast prostheses by dip forming and curing a silicone outer shell, and then filling the cured shell with saline, gel or other material. The shell is typically formed by dipping a mandrel into a bath of solvent dispersed silicone, and then devolatilizing the solvent from the applied layer of silicone elastomer after the dipping process. Additional layers of silicone, having the same or different properties, may be built up on the mandrel. For example, a base layer will be deposited, followed by a barrier layer, and then followed by another finishing layer.

After the shell has been formed, the silicone layers, while devolatilized, are not yet cured into a permanent form. Curing is typically carried out in a convection oven which may take several hours to ensure that the shell is completely cured. Alternatively, infrared heat transfer has been used effectively, but temperature control is challenging and safe time cycles are typically over 1 hour.

A silicone breast prostheses having a porous or textured outer surface is believed to evoke a reduced incidence and severity of capsular contracture, which is the formation of an oriented myelinated collagen biological capsule around the implant. Capsular contracture occurs when myelinated collagen films contract and the implant becomes visibly spherical and very firm. Various methods have been used to texture the surface of a silicone breast prosthesis. In one method, a layer of silicone or urethane foam is formed on the top surface of the implant. In another prior method, the surface of a mold or mandrel is etched so that the etched pattern is transmitted to the shell of the prosthesis when the shell is formed in the mold or on the mandrel. In yet another prior method, a soluble material, such as, for example, a salt, is incorporated into outer layer of the silicone shell. The soluble salt material is then removed after curing the shell, thus leaving voids where the salt used to be after the shell is cured.

What has been needed, and heretofore unavailable, is a low cost highly efficient process for curing a thin silicone sheet, such as the shell of a silicone breast prosthesis more quickly than can be accomplished using a convection oven or infrared heater. It is further desireable to have a process capable of combining efficient cure while simultaneously dissolving soluble material incorporated into the uncured shell to provide a textured shell; thus reducing the time of manufacture, reducing the number of manufacturing steps, and reducing damage to the thin silicone sheet or shell caused by the multiple processing steps currently needed to cure a shell and dissolve the soluble material from the shell. The present invention satisfies these and other needs.

SUMMARY OF THE INVENTION

In its most general aspect, the invention includes a system and method for efficiently curing a thin dipped formed silicone elastomer shell by immersing the uncured elastomer into a hot liquid bath for a predetermined period of time. The hot liquid bath will generally be heated to a temperature in the range of 95 degrees centigrade to 160 degrees centigrade. Curing the silicone shell in this manner results in a fully cured shell in far less time than is required for curing the same prosthesis in a convection oven or IR system.

Typically, the invention includes a system and method for curing a thin silicone shell mounted on a mandrel by immersing the prosthesis shell and mandrel into a hot liquid bath. Such a method is advantageous in that it eliminated the need to remove the delicate uncured silicone shell from the mandrel before curing the shell in a convection oven.

In still another general aspect, the invention includes a system and method wherein a silicone prosthesis shell is formed on a mandrel by dip forming layers of silicone on the mandrel, and then incorporating a soluble material, such as a salt, into one or more layers of the shell, and then curing the shell on the mandrel by immersing the shell and mandrel into a hot bath of liquid that will dissolve or otherwise remove salt or other soluble particles. The advantage of this aspect of the invention is that it provides for simultaneous curing of the shell and dissolution of the soluble material, providing a prosthesis shell that has a textured surface.

In yet another aspect, the method includes curing a silicone shell by immersing the shell while still on its mandrel in a series of baths to prevent thermal shock or to ensure complete removal of any solvent remaining in the uncured silicone shell. In one alternative aspect, the shell and mandrel may be immersed in a first bath having a temperature of, for example, 60 degrees centigrade, and then placed in a second bath having a temperature of, for example, 130 degrees centigrade.

In still another aspect, the method includes immersing the cured silicone shell into a “cold” bath to quickly cool the cured shell and mandrel to allow for further processing or handling of the shell and mandrel.

In still another aspect, the system and method includes forming a silicone shell on a mandrel, immersing the uncured silicone shell and mandrel in a hot liquid bath to cure the silicone elastomer shell, and then applying one or more additional layers of uncured silicone to the cured silicone shell, incorporating a soluble particulate material into the uncured layers of silicone, and then immersing the coated shell and mandrel into a bath of hot liquid to cure the additional layer or layers of silicone and to dissolve the soluble particulate material from the additional layer or layers of silicone to produce a textured surface on the prosthesis shell. In one alternative aspect, the cured shell and mandrel may be immersed in a cold liquid bath after the initial hot liquid bath to cool the shell and mandrel before the additional one or more layers of uncured silicone are applied to the cooled, cured, silicone shell.

In another aspect, the present invention includes a method for manufacturing a thin sheet of prosthetic material, comprising: applying a solution of uncured prosthetic material to a mold; and curing the applied uncured prosthetic material by immersing the mold and applied uncured prosthetic material in a hot liquid bath. In one alternative aspect, the uncured prosthetic material is silicone. In another alternative aspect, the mold is a mandrel.

In yet another aspect, the liquid in the hot liquid bath is water having a temperature greater than 50 degrees centigrade. In an alternative aspect, the liquid in the hot liquid bath is a liquid having a low solubility in uncured silicone.

In still another alternative aspect, the liquid has a temperature in the range of 120 to 150 degrees centigrade. In an alternative aspect, the temperature is 130 degrees centigrade. In another alternative aspect, the liquid has a temperature in the range of 120 to 150 degrees centigrade. In still another alternative aspect, the temperature is 110 to 140 degrees centigrade.

In another aspect, the liquid is a non-toxic liquid. In one alternative aspect, the non-toxic liquid is selected from the group consisting of propylene glycol, polyethylene glycol, esterified polyethylene glycol and fatty acid esters. In another alternative aspect, the liquid is a eutectic salt having a melting point of less than 200 degrees centigrade. In yet another alternative aspect, the liquid is a eutectic metal having a melting point of less than 200 degrees centigrade.

In still another aspect, applying the solution of uncured prosthetic material forms an uncured breast implant shell. In one alternative aspect, applying the solution of uncured prosthetic material includes dipping the mold into the solution of uncured prosthetic material. In another alternative aspect, dipping the mold into the solution of uncured prosthetic material forms a layer of uncured prosthetic material on the mold having a thickness of less than 1 millimeter. In still another alternative aspect, applying the solution of uncured prosthetic material includes spraying the solution of uncured prosthetic material onto the mold.

In a further aspect, the method further comprises applying a second layer of uncured prosthetic material to the mold; and curing the second layer of uncured prosthetic material by immersing the mold and uncured second layer of uncured prosthetic material in a hot liquid bath.

In another further aspect, the second layer of uncured prosthetic material includes texture components. In a still further aspect, curing the second layer of uncured prosthetic material by immersing the mold and uncured second layer into the hot liquid bath also dissolves the texturing components from the uncured second layer such that the cured second layer has a textured outer surface.

In a still further aspect, the method includes mechanically applying a texture to a top surface of the applied uncured prosthetic material before immersing the applied uncured prosthetic material and mold into the hot liquid bath.

Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an embodiment of a process for applying a liquid prosthetic material to a mold or mandrel.

FIG. 2 is a sectional side view of an embodiment of a process for curing the liquid prosthetic material applied to the mold or mandrel of FIG. 1 by immersing the mold or mandrel into a hot liquid bath.

FIG. 3 is a perspective view of a layer of uncured prosthetic material including texture components formed over a cured layer of prosthetic material applied to a mold or mandrel.

FIG. 4 is a perspective view of the embodiment of FIG. 3 after the mold or mandrel has been immersed in a hot liquid bath to cure the layer of prosthetic material and dissolve the texture components.

FIG. 5 is a flow chart illustrating a process in accordance with an embodiment of the invention.

FIG. 6 is a flow chart illustrating a process for forming multiple layers of prosthetic material in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, in which like reference numerals indicate like or corresponding elements among the several figures, there is shown in FIG. 1 an embodiment of the invention wherein a mandrel 10 is dip coated with a liquid material 15, such as, for example, silicone elastomer base, that is dripped or sprayed onto the mandrel from delivery assembly 20. Excess liquid material 15 may be caught in basin 25. Alternatively, the mandrel may be dipped into a bath of the liquid material, or the shell may be formed on or in a mold.

The liquid material will then typically be exposed to a stream of air (not shown) to devolatilize solvent in the applied liquid material. The mandrel may then be again exposed to the delivery assembly 20 again to form an additional layer of material on the mandrel. These steps are repeated until a desired thickness of the shell has been achieved.

When the prosthesis shell is a desired thickness, as depicted in FIG. 2, the mandrel 10 and uncured shell 110 are placed in a bath 100 of hot liquid 105. The temperature of the hot liquid 105 may be, for example, in the range of 50 degrees centigrade to 150 degrees centigrade, and preferably 130 degrees centigrade. The mandrel and shell will typically be immersed in the hot liquid 105 for a period of time ranging from two minutes to ten or more minutes, and preferably immersed for five minutes, depending on how long it takes to devolatilize and cure the shell material.

In some embodiments, it may be desirable to form additional layers of material on the shell. In such cases, after the first layer is cured in the hot liquid bath, the mandrel and shell may be rinsed and dried, although those steps may not be necessary, and then the additional layers are formed on the shell as discussed above. The additional layer or layers may be formed from the same liquid material as a previous layer, or the additional layer or layers may be formed from a different liquid material having different properties than a previous layer or layers. For example, a “barrier” layer may be formed on top of a “base” layer to prevent bleed through of materials used to fill the shell to form the ultimate prosthesis. Each time a layer is farmed, the uncured layer may be cured by immersing the mandrel and shell into the hot liquid bath for a period of time selected to ensure that the uncured layer of the shell is cured.

For a variety of reasons, it may be desirable to cure the shell in a series of hot liquid baths. For example, in one embodiment, the mandrel and uncured shell may be first placed in a hot liquid bath at a temperature of 50-60 degrees centigrade to prevent damage to the shell or mandrel due to thermal shock, or the ensure that the shell is completely devolatilized before the mandrel and uncured shell are then placed in a second hot bath. As will be apparent to one skilled in the art, this process may be repeated several times, using a series of baths of increasing temperature, depending upon the material or materials being used to form the shell.

In some embodiments, it may be desirable to rinse the mandrel and shell after they are removed from the hot liquid bath to remove any residual hot liquid that may cling to the mandrel and cured shell. In some embodiments, the rinse step may include immersion in a cold liquid bath to quickly remove residual heat from the mandrel and cured shell to allow for more rapid subsequent processing of the shell or handling of the mandrel. The temperature of the cold bath will typically be less than 50 degrees centigrade, and preferably 25 degrees centigrade.

The liquid of the hot and cold baths may be, for example, water. In other embodiments, the liquid may be selected to be compatible with the shell and mandrel materials. For example, the liquid used in the baths may be chemical with low solubility in uncured silicone, such as, for example, a non-toxic chemical such as a glycol derivative, including propylene glycol and polyethylene glycol, esterified polyethylene glycol, fatty acid esters and the like. The liquid may also be a eutectic salt or metal with a melting point of less than 200 degrees centigrade, and having a melting point preferably below 130 degrees centigrade.

Where a prosthesis is desired to have a textured surface, a texture component may be added to the liquid material from which the shell is formed. FIG. 3 depicts an embodiment wherein a first layer 210 has been formed on a mandrel 205. First layer 210 has been cured by immersing the mandrel and the first layer in a hot liquid bath as described above.

The mandrel and cured first layer may then be rinsed or immersed in a cold bath to reduce the temperature of the mandrel and cured shell as well as to remove any residual hot liquid from the hot liquid bath. A second layer of material 215 containing texture components 220 is then formed on top of the first, cured, layer by dripping or spraying the material 215 containing texture components onto the mandrel and cured first layer.

Once a desired thickness of the second, uncured layer of material including texture components has been achieved, the mandrel and shell are immersed in a hot liquid bath. During the immersion in the hot liquid, the second material 215 is cured, and the texture components contained in the second material are dissolved. For example, where the texture component is a salt, the hot liquid is chosen so that the hot liquid does not dissolve the uncured shell material, but does dissolve the texture component. In one embodiment, the hot liquid may be water, which does not dissolve silicone, but which does dissolve salt used as a texture component.

The texture components may be, for example, various types of salt of dissolvable plastic particles. The size of the texture components are selected so as to form a surface of the shell have a particular texture topography. For example, the texture components may be between 100 and 500 microns in diameter.

Alternatively, the last layer of the shell to be cured may also be textured by applying a roll or stamp to the uncured surface of the shell, and then immersing the uncured shell in to the hot liquid bath. In this manner the texture of the surface of the roll or stamp may be transferred to the uncured shell and then “frozen” on the surface of the shell when the shell is cured in the hot liquid bath.

FIG. 4 illustrates a shell 300 on mandrel 205 having a surface layer 305 that has a texture 310 imparted to the surface of the shell using the various embodiments of the invention described above. Among the advantages of the various embodiments of the system and method of the present invention is that curing the shell and dissolving the texture component in a single step simplifies the processing of the shell, eliminates additional handling of the shell and mandrel, and improves process efficiency, which also reduces the cost of manufacturing the prosthesis.

FIG. 5 is a flow chart illustrating the steps of one embodiment of a process 400 that may be used to form a prosthesis shell in accordance with the various embodiments of the present invention. In box 405, a shell is formed on a mandrel. In box 410, the shell and mandrel are immersed in a hot liquid bath to cure the shell material. The cured shell and mandrel are rinsed or immersed in a liquid bath in box 415. The rinse liquid or bath liquid may be relatively cold, such as, for example, about 25 degrees centigrade, to remove residual liquid or heat transfer medium remaining on the cured shell and mandrel from the hot liquid bath. The cured shell may then be dried in box 420.

FIG. 6 is a flow chart illustrating the steps of one embodiment of a process 500 that may be used to form a prosthesis shell having two or more layers, which, in some embodiments, each layer may be formed of a different material. A first layer is formed on a mandrel in box 505. That first layer is cured by immersing the mandrel and first layer in a hot liquid bath 510. The cured shell and mandrel are then immersed in a cool liquid bath 515. Alternatively, the, cured shell and mandrel may be sprayed with a cooled liquid, and then dried.

A second layer of material, which may be a different material than used to form the first layer, is then formed on the cured shell in box 520. In some embodiments, this second layer may be a barrier layer, or it may include texture components for forming a textured surface, or both.

The mandrel and shell having the second, uncured, layer is then immersed in a hot liquid bath in box 525. The uncured second layer is then cured by the hot liquid, and, if the second layer includes texture components, the texture components are dissolved by the hot liquid.

The mandrel and cured shell may then be immersed into a cool bath as in box 530, or the mandrel and shell may be otherwise rinsed with a liquid, which may be cool in temperature. Where needed, the shell may also be rinsed in box 535, and dried in box 540.

While the embodiment of FIG. 6 has been discussed in reference to a shell having two layers, those skilled in the art will appreciate that additional layers may be added to the shell by repeating the various steps of the process as need to achieve a shell have a desired thickness or surface properties.

It should also be understood that, while the various embodiments of the present invention have been described in relation to forming a prosthesis shell, the principles of the invention also apply to forming thin sheets of a material on a base mold, and are within the intended scope of the invention.

While particular embodiments of the present invention have been described, it is understood that various different modifications within the scope and spirit of the invention are possible. The invention is limited only by the scope of the appended claims. 

I Claim:
 1. A method for manufacturing a thin sheet of prosthetic material, comprising: applying a solution of uncured prosthetic material to a mold; and curing the applied uncured prosthetic material by immersing the mold and applied uncured prosthetic material in a hot liquid bath.
 2. The method of claim 1, wherein the uncured prosthetic material is silicone.
 3. The method of claim 1, wherein the mold is a mandrel.
 4. The method of claim 1, wherein the liquid in the hot liquid bath is water having a temperature greater than 50 degrees centigrade.
 5. The method of claim 1, wherein the liquid in the hot liquid bath is a liquid having a low solubility in uncured silicone.
 6. The method of claim 1, wherein the liquid has a temperature in the range of 120 to 150 degrees centigrade.
 7. The method of claim 6, wherein the temperature is 130 degrees centigrade.
 8. The method of claim 5, wherein the liquid has a temperature in the range of 120 to 150 degrees centigrade.
 9. The method of claim 8, wherein the temperature is 110 to 140 degrees centigrade.
 10. The method of claim 5, wherein the liquid is a non-toxic liquid.
 11. The method of claim 10, wherein the non-toxic liquid is selected from the group consisting of propylene glycol, polyethylene glycol, esterified polyethylene glycol and fatty acid esters.
 12. The method of claim 1, wherein the liquid is a eutectic salt having a melting point of less than 200 degrees centigrade.
 13. The method of claim 1, wherein the liquid is a eutectic metal having a melting point of less than 200 degrees centigrade.
 14. The method of claim 1, wherein applying the solution of uncured prosthetic material forms an uncured breast implant shell.
 15. The method of claim 1, wherein applying the solution of uncured prosthetic material includes dipping the mold into the solution of uncured prosthetic material.
 16. The method of claim 15, wherein dipping the mold into the solution of uncured prosthetic material forms a layer of uncured prosthetic material on the mold having a thickness of less than 1 millimeter.
 17. The method of claim 1, wherein applying the solution of uncured prosthetic material includes spraying the solution of uncured prosthetic material onto the mold.
 18. The method of claim 1, further comprising: applying a second layer of uncured prosthetic material to the mold; and curing the second layer of uncured prosthetic material by immersing the mold and uncured second layer of uncured prosthetic material in a hot liquid bath.
 19. The method of claim 18, wherein the second layer of uncured prosthetic material includes texture components.
 20. The method of claim 19, wherein curing the second layer of uncured prosthetic material by immersing the mold and uncured second layer into the hot liquid bath also dissolves the texturing components from the uncured second layer such that the cured second layer has a textured outer surface.
 21. The method of claim 1, further comprising: mechanically applying a texture to a top surface of the applied uncured prosthetic material before immersing the applied uncured prosthetic material and mold into the hot liquid bath. 